The present invention relates to needle-like zinc carbonate useful as a filler or a precursor of needle-like zinc oxide, process for producing it and an electroconductive powder produced by firing zinc carbonate.
Processes for producing needle-like zinc oxide, among needle-like zinc compounds, are well-known as described in, for example, Japanese Patent Unexamined Published Application (hereinafter referred to as `J.P. KOKAI`) Nos. 50-6597, 56-120518 and 57-205320. However, they have problems in that they necessitate a complicated apparatus and that the product has only a low concentration.
Further, although zinc carbonate can be converted into zinc oxide by firing, no process for producing neddle-like zinc carbonate has heretofore been known.
On the other hand, processes for producing unshaped zinc carbonate have already been known. For example, J.P. KOKAI No. 60-200826 discloses a process for producing basic zinc carbonate by bubbling carbon dioxide or a carbon dioxide-containing substance into an aqueous slurry of zinc oxide. However, the needle-like product cannot be obtained by this process.
No process has been known for producing needle-like zinc carbonate containing aluminum as the dopant.
On the other hand, a white or whitish electroconductive filler for resins and paints capable of coloring them as desired has been demanded. Various investigations has been made for the purpose of satisfying such a demand. Electroconductive zinc oxide containing a doping agent such as Al, Ga or Ge was proposed since zinc oxide is essentially a white semi-conductor. In particular, those containing Al, Ga or In as the doping agent (U.S. Pat. No. 3,538,022), those containing Ge or Sn (U.S. Pat. No. 3,538,023), those containing Al (J.P. KOKAI No. 54-161598) and those containing Al, Ti or Sn (J.P. KOKAI No. 58-161923) were proposed. Although there are thus known the processes for reducing the volume resistivity of ZnO by adding Al, Ga, Sn, Ge or In thereto, the products obtained by these process are in the form of a globular or unshaped powder and, therefore, a large amount thereof is necessitated for imparting electroconductivity to resins.
Further although processes for producing needle-like or platy ZnO are known, the product does not contain any doping agent such as Al and are used for purposes different from the imparting of electroconductivity.
The processes for producing platy ZnO include a process disclosed in J.P. KOKAI No. 53-83996 and processes for producing needle-like ZnO include those described above.